Recently, we proposed that a single model could account for a large body of behavioral data in numerous motor adaptation paradigms. The idea was that motor memory is supported by at least two interacting processes: a fast process that strongly learns from motor error but rapidly forgets, and a slow process that only gradually learns from error but has long-term retention. The main purpose of this research is to uncover the time and error-dependent properties of these putative processes and to ask whether there is a link between these processes and the functions of the cerebellum and the primary motor cortex. First, psychophysical experiments will be employed to map out the time and error sensitivity of the "fast" and "slow" states of motor memory. Second, singe pulse transcranial magnetic stimulation (TMS) will be applied during adaptation to investigate the role of the primary motor cortex in the putative fast and slow processes. We hypothesize that disruption of M1 primarily disrupts the slow system. Third, to better understand the role of the cerebellum in motor learning, the onset of the perturbation during adaptation will be manipulated to preferentially engage the slow (gradual onset perturbation) or fast (sudden onset perturbation) system in cerebellar disease patients. If the fast adaptive process is contained within or controlled by the cerebellum, preferentially engaging the slow system will allow adaptation to occur with a slow rate of forgetting, while a sudden onset will prevent learning. Finally, we will examine patients who have a deep brain stimulator (DBS) implanted in their cerebellar thalamus to ask whether disruption of this thalamic relay from the cerebellum to the motor cortex disrupts the fast, slow, or both systems. PUBLIC HEALTH RELEVANCE Our ability to make accurate movements is due to a constant process of calibration and adaptation in our motor system. My experiments aim to better understand the mechanisms with which the brain adapts to errors in our movements. A better understanding of this process can help development of new rehabilitation techniques and procedures for patients following stroke or implantation of DBS. [unreadable] [unreadable] [unreadable]